DDX1 (DEAD (Asp-Glu-Ala-Asp) box polypeptide 1)

	Genomic organization of human DDX1 gene. Boxes and connecting lines indicate exons (omitted in the middle part) and introns, respectively. The ATG transcription initiation site is located in exon 2.
Description	DDX1 gene is located in an approximately 40 kb chromosomal DNA region of 2p24.3 containing at least 27 exons. There are alternatively used exons for exon 2, 16, 19, 21, 23 and 27.
Transcription	Size of the major mRNA is 2.7 kb.

	Diagram of conserved motifs among DEAD box RNA helicase family proteins.
Description	DDX1 protein is a putative RNA helicase containing the characteristic Asp-Glu-Ala-Asp (DEAD) conserved sequence motif (Linder et al., 1989). It is composed of 740 amino acid residues (82432 Da). Proteins of this family (more than 30 from bacteria to humans) have been described to be implicated in a number of cellular processes involving alteration of RNA secondary structure such as translational initiation, nuclear and mitochondrial RNA splicing, and ribosome/spliceosome assembly (Rocak and Linder, 2004).
Expression	DDX1 mRNA is widely expressed in many tissues, but its expression level is highest in testis (Tanaka et al., 2009). DDX1 level tends to be higher in tumor-derived cells than in normal tissues.
Localisation	DDX1 protein is localized both in the cytoplasm and nucleus of DDX1 gene-amplified neuroblastoma and retinoblastoma cell lines, but mainly located in the nucleus of normal fibroblasts (Godbout et al., 1998).
Function	DDX1 is believed to regulate translational initiation, nuclear hnRNA splicing, ribosome/spliceosome assembly, and mRNA synthesis as a putative ATP-dependent RNA helicase. DDX1 is associated with a pre-mRNA 3'-end cleavage protein CstF-64 (Bleoo et al., 2001) and heterogeneous nuclear ribonucleoprotein K (hnRNP K) (Chen et al., 2002). hnRNP-K is involved in cell migration and cytoplasmic accumulation of hnRNP-K is crucial for metastasis (Inoue et al., 2007). It was reported that DDX1 interacts with nuclear diffusion inhibitory signal (NIS) motif of HIV-1 Rev protein in human astrocytes. Accumulation of DDX1 in astrocytes changed sub-cellular distribution of Rev from nuclear to cytoplasmic (Fang et al., 2005). More recently, it was reported that DDX1 is recruited to the sites of DNA double strand breaks in cells exposed to ionizing radiation and removes single stranded RNAs to facilitate the repair reaction of transcriptionally active regions of the genome (Li et al., 2008). In retinoblastoma and neuroblastoma cell lines, co-amplification of DDX1 and the proto-oncogene MYCN has been demonstrated (Godbout and Squire, 1993; Godbout et al., 1998). Similar gene amplification of the genomic region containing DDX1 and MYCN was observed in alveolar rhabdomyosarcoma samples (Barr et al., 2009) and Wilms tumor-derived cells (Noguera et al., 2010). Elevated expression of DDX1 mRNA was reported to be a prognostic marker for early recurrence in primary breast cancer (Germain et al., 2010). Recently, it was demonstrated that DDX1 is essential for the solid tumor formation of a human testicular tumor cell line NEC8 in nude mice (Tanaka et al., 2009). In this case, DDX1 directly bound to the -348 and -329 promoter region of the cyclin-D2 gene and enhanced its transcription. Furthermore, siRNA-mediated knockdown of DDX1 resulted in coordinated down-regulation of stem cell-associated genes located in chromosomal region 12p13. Therefore, DDX1 may function as an essential transcriptional activator for the tumorigenic capacity of testicular germ line tumor-derived cells. In agreement, DDX1 promotes the proliferation of JC virus via the transcriptional activation of its viral promoter (Sunden et al., 2007). It was also reported that DDX1 acts as a co-activator to enhance NF-kappaB-mediated transcription (Ishaq et al., 2009).

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